The present invention relates to nebulizers and more particularly to an improved reservoir arrangement for containing a liquid to be nebulized.
Nebulizers, or atomizers, are devices that generate a fine spray or aerosol. A particularly useful application for nebulizers is to convert aqueous drug solutions, or suspensions with non-dissolved particles, into an aerosol of small droplets that can thereafter be inhaled to administer the drug to a subject during breathing. Such inhalation treatment is highly effective for conditions effecting the subject's respiratory organs. Further, since the lungs are close to the heart and the blood circulatory system of the body, drug administration by inhalation provides an effective and rapid delivery system to all organs of the body.
In many cases, the subject breathes with the aid of a respiratory ventilator. A typical ventilator has a breathing circuit comprising an inhalation limb and an exhalation limb connected to two arms of a Y-connector. The third arm of the Y-connector is connected via a patient limb to a mouth piece, mask, or endotracheal tube for the subject. The ventilator provides a desired degree of assistance to the breathing of the subject during the inhalation phase of the respiratory cycle. The contraction of the subject's lungs discharges gas through the exhalation limb during exhalation. To achieve the maximum physiological effect for the subject and to avoid wastage of the drug, the nebulizing action of the nebulizer is synchronized with the inspiratory phase of the respiratory cycle. A typical example of a nebulizer arrangement is shown in U.S. patent application Ser. No. 09/397,529, filed Sep. 16, 1999; Ser. No. 09/547,523, filed Apr. 12, 2000; and Ser. No. 09/699,049, filed Oct. 30, 2000 and European Patent Applications 311,773.6, filed Dec. 29, 2000 and 311,778.5, filed Dec. 29, 2000 which applications are incorporated herein by reference to the extent permitted. In nebulizers of the type shown in the foregoing U.S. and European patent applications, the liquid is converted to an aerosol by the action of a vibrating element, such as a piezoelectric element. The supply of liquid from a liquid reservoir to the nebulizing element is controlled by a valve. The liquid reservoir is pressurized to cause the liquid to flow through the valve to the element when the valve is open.
In order to ensure maximum penetration depth of a nebulized drug into the lungs of the subject, the gas volume in the breathing circuit between the nebulizer and the lung should be minimized. To this end, the nebulizer is typically positioned near the patient mouth piece, mask, or endotracheal tube, i.e., in the patient limb of the breathing circuit described above. However, for surgical and intensive care patients, the area around the nose, mouth, neck and upper chest is often critical to the care of the patient and/or crowded with other equipment. The overall size of the nebulizer, including its liquid reservoir, thus becomes very important. A liquid container remote from the nebulizer may be used to reduce the size of the nebulizer. However, if a small volume of drug is to be delivered, such an arrangement can be disadvantageous because of the amount of drug required to fill the liquid supply line between the container and the nebulizer and the residuum of drug left in the supply line. A local liquid reservoir mounted on the nebulizer would thus be advantageous in such circumstances.
Such a local liquid reservoir for a nebulizer typically comprises two compartments separated by a moving wall. One compartment contains the liquid drug. The other compartment contains a pressurizing gas. The moving wall ensures that the drug is not contaminated by the gas. The liquid compartment is filled with the drug by a syringe through a filling port. A syringe may also be used to pressurize the gas compartment. The reservoir so filled is mounted on the nebulizer to supply liquid to the vibrating element of the nebulizer.
However, in such a local liquid reservoir, the gas compartment adds to the overall size of the reservoir. As noted above, size is a serious concern for certain uses of the nebulizer. Also, pressurization of the gas compartment is an additional maneuver required when using a nebulizer of this type.
Another requirement for a local reservoir for a nebulizer is that it be able to generate the necessary pressure to deliver liquid from the liquid compartment to the nebulizing element, including cases in which the inhalation limb and patient limb are pressurized by the ventilator to provide breathing gases to the subject. It is also desirable that the liquid reservoir be capable of supplying the liquid independently of the position or orientation of the nebulizer. To ensure that a proper drug dosage is administered to the subject and to avoid wastage of drug, it is desirable that the reservoir be capable of being completely emptied. It should be easy to fill the reservoir. At the end of the drug administration, the reservoir should be easy to clean or dispose of. And, as noted above, the reservoir should be as small as possible, commensurate with the volume of liquid to be delivered to the subject.